Interengaging splined shafts fulfil this function but they require lubrication if there is much movement between the two shafts and indeed even if there is only a little. If there is normally only a little movement a step can form on the splines preventing or at least hindering further axial movement on the few occasions this may occur. Also, within normal manufacturing tolerances there is inevitably a certain degree of lost motion between the two shafts which thus allows a backlash to develop between them. A presently available coupling comprising membranes disposed radially between interjacent flanges on the two shafts solves many of these drawbacks. It can be built torsionally rigid within wide tolerances; it requires no lubrication and it does not wear. Furthermore it can accept angular misalignment between the shafts. Such a coupling is disclosed in U.S. Pat. No. 4,196,597.
However beyond fairly small limits of axial movement the axial loads on the shafts increase considerably. In other words these membranes do not allow adequate axial movement for some applications.
Joining couplings together does not help if the coupling is rendered laterally unstable.
It is an object of this invention therefore to provide a membrane-type coupling having both lateral stability and increased axial movement capability.